Integrated circuits may be fabricated on semiconductor wafers which are processed in lots. The wafers in a lot are commonly transported and stored in a wafer carrier with a capacity of, typically, 25 wafers. An integrated circuit fabrication line may run at a desired level of efficiency if all lots have a number of wafers equal to the capacity of the wafer carriers, that is, if the fabrication equipment is always processing full wafer carriers. However, frequently a lot may have fewer wafers than the capacity of the wafer carrier. Lots with fewer wafers than the wafer carrier capacity may come about because wafers are scrapped during the fabrication sequence, or because only a few wafers are needed to fill a customer order. Lots with fewer wafers than the wafer carrier capacity may cause inefficiency in the fabrication line, because some fabrication equipment cannot process partially filled wafer carriers at the same rate, in wafers per hour, as full wafer carriers.